1. Field of the Invention
The invention relates to the purification and recovery from a reaction mixture of the alkaline earth metal salt of 2,2'-oxydisuccinic acid by a process which produces the salt in very high purity while substantially avoiding contamination of the reaction mixture with undesirable reaction products and solvents. 2,2'-oxydisuccinic acid and salts thereof are effective sequestering agents and are useful as builders in detergent compositions for household, institutional and industrial use.
2. Related Art
2,2'-oxydisuccinic acid (ODS) and salts thereof are known to have utility as sequestering agents and detergent builders. A disadvantage of ODS and its salts as detergent builders is that they may be relatively expensive to prepare.
U.S. Pat. No. 3,128,287 to Berg discloses a preparation of ODS salt by admixing maleic acid with an excess of calcium, barium, magnesium or strontium hydroxide in the presence of water, then heating the reaction mixture from about one day to about one month at temperatures ranging from 50.degree. C. to reflux temperatures. The process yields a mixture of malic acid and ODS. Berg's Example I teaches a preparation of ODS, where an aqueous mixture of maleic anhydride and calcium hydroxide is reacted at reflux (100.degree. C.) for 4 days. Subsequently, ODS salt is isolated from the product containing ODS and malic acid salts by various methods.
U.S. Pat. No. 3,635,830 to Lamberti et al., discloses a process for the preparation of ODS based on the process of Berg. The patent teaches separation/purification of two diastereoisomeric forms of ODS obtained by the Berg process. The patent also discloses detergent compositions comprising ODS or salts thereof as detergent builders.
U.S. Pat. No. 5,030,751 to Lamberti discloses methods of making mixed ODS/CMOS salts and separation by solvents.
U.S. Pat. No. 5,068,420 to Kreczmer discloses alkaline alcohol extraction to purify ether carboxylate salts.
U.S. Pat. No. 4,959,496 to Crutchfield discloses processes for the preparation of ether carboxylate where unreacted starting acids are recovered.
U.S. Pat. No. 3,914,297 to Lamberti employs ion exchange resins and acetone to recover various ether polycarboxylate salts.
A workable and cost-efficient production of ODS salt must be directed towards optimizing the process conditions in such a manner that the salts can be easily obtained in high yield without having to resort to expensive solvents which also must be disposed of after use. There have been different approaches to the problem of producing ODS in high yield at a low cost. However, none of these approaches has been completely satisfactory.
Accordingly, it is an object of the present invention to provide a process which produces the alkaline earth metal salt of ODS in high purity and high yield.
This and other objects and advantages will appear as the description proceeds.